Photosensitive elements which can be used in image-reproduction processes are well-known in the graphic arts industry. Typically, the elements are exposed to actinic radiation through an image-bearing transparency, such as a color separation transparency, to produce an image which is either a positive or negative with respect to the transparency used. Positive-working elements produce an image which is a duplicate of the transparency through which they are exposed. That is, the colored regions of the transparency are colored in the imaged element and the uncolored regions in the transparency are uncolored in the imaged element. Negative-working elements produce an image that is the reverse of the transparency through which they are exposed. That is, the colored regions of the transparency are uncolored in the imaged element and the uncolored regions in the transparency are colored in the imaged element. Ordinarily, a positive-working element is exposed through a positive transparency to produce a positive image and a negative working element is exposed through a negative transparency to produce a positive image. Following imagewise exposure, the photosensitive elements may be developed by washing out the soluble image areas, by peeling apart, by toning with a colorant, or combinations of these techniques.
Precolored diazo based imaging elements are well known in the art. These elements, however, have the disadvantage of requiring either an organic solvent or aqueous base for coating and/or development. Precolored diazo based imaging elements which are developed in a mixture of 1-propanol and water are disclosed, for example, in Van Beusekom, U.S. Pat. No. 3,671,236; Cederburg, U.S. Pat. No. 4,656,114; and Sachi, U.S. Pat. No. 4,666,817. An element which can be developed in base is disclosed in Krech, U.S. Pat. No. 4,260,673. Frequently, the use of an aqueous base or organic solvent is undesirable due to flammability, toxicity, corrosion and/or waste disposal considerations.
Platzer, U.S. Pat. No. 4,751,166, discloses a precolored negative working diazo image-forming element containing a binder selected from the group consisting of a polyvinyl butyral polymer and a styrene-maleic anhydride polymer. The element is developable in water containing surfactants such as (1) sodium decyl sulfate, disodium phosphate and sodium metasilicate, or (2) monosodium phosphate, trisodium phosphate, and sodium tetradecyl sulfate.
Mino, U.S. Pat. No. 4,783,390, discloses a multicolor diazo image-forming element comprising at least two colorant-containing photosensitive layers on a support. Each photosensitive layer is formed from a water-soluble, organic solvent-insoluble diazo resin; a water-soluble resin having photocrosslinking ability with the diazo resin; and a water dispersible colorant. Between each photosensitive layer and the next adjacent photosensitive layer is an intermediate layer formed from a hydrophobic, water-resistant organic solvent-softenable resin. Although the photosensitive layer can be developed by water, the intermediate layer is removed by an organic solvent. In addition, the image formed on the upper photosensitive layer is sometimes washed away when the lower layers are developed. The material is limited to the reproduction of continuous tone images.
Maruyama, Japanese Patent Application 61-292,295, discloses a water-developable composition composed of a diazo resin, polyvinyl pyrrolidone having a mean molecular weight of about 20,000 to 1,000,000 and a colorant. Although the composition is water-developable, it has the disadvantage of being coated from organic solvents.
There is a need for a photosensitive element which can be both coated from, and developed in water, thereby eliminating the requirement of organic solvents, surfactants, and aqueous bases in both the manufacturing process and the process of use. This element should be capable of reproducing both half tone and continuous tone images.